(1) Field of the Invention
This invention pertains to an illuminated spirit bubble vial and, in particular, to a trademan's level incorporating such a vial.
(2) Description of the Prior Art
Over the years, wherever spirit bubble levels have been encountered, e.g., in carpenter's and other tradesperson's levels, in various instruments such as sextants and octants, on artillery pieces, and on various industrial equipment which must be leveled, reading the spirit bubble level has sometimes been a most difficult problem. Oftentimes, the equipment incorporating the level is located in an area which is provided with poor lighting, or in which no lighting exists at all, or the level must be observed at night, or during a time when natural lighting is poor.
Working conditions encountered by carpenters, masons, electricians, steam fitters and allied tradespersons in building construction and maintenance are such that it is not unusual for them to be required to read a level under poor lighting conditions. This problem is somewhat compounded in the event the work against which the level is placed is of a dark color. And cloudy or rainy days cause additional problems.
As a result of the problems encountered in reading spirit or bubble levels, substantial efforts have been devoted over the years to the development of spirit level constructions with a view to enhancing or intensifying the bubble image. In some cases this has merely involved the providing of a luminescent, color contrasting, or reflecting background against which the bubble level is viewed. However, in a substantial number of cases, efforts have been made to provide illumination to the spirit level cavity.
None of the lighted levels of which we are aware, however, prior to our invention of a lighted level, disclosed in U.S. patent application Ser. No. 219,996, filed Dec. 23, 1980, now abandoned, the disclosure of which is herein incorporated, provided entirely satisfactory performance. All of the earlier lighted levels, as far as we know, used flash light bulbs. In many instances, however, the location of the light bulb was such that the spirit bulb was not well lighted. In some cases the location of the light bulb actually interferred with reading the level, as the light bulb was located directly in the observer's field of vision. Sometimes the spirit vials were not uniformly lighted; for example, where a light bulb was located on one side of a pair of spirit vials, one vial was relatively well lighted, and the other hardly at all.
As will be well appreciated, however, probably the most serious problem with lighted levels utilizing light bulbs as the source of light is that the bulbs have to be periodically replaced. Light bulbs burn out, and with little or no warning. A level with a burned out bulb can be even more useless to a carpenter or other tradesperson than a level that is not of the so-called "illuminated type". This is because the worker is depending on its lighting facility in a poorly lighted area and accordingly may not come prepared with other lighting means, e.g., a flash light, in the event of a failure to light. A match, moreover, may or may not be handy. Of consequence also, and in addition to bulbs burning out, is the fact that light bulbs are subject to breakage, in the event of a severe shock, if the level is accidentally dropped.
Oftentimes the construction of the level has been such that burned out, or broken, light bulbs have not been easily and readily replaced. In any event, the tradesperson can only be assured of having an illuminated level which always lights by always carrying an inventory of spare light bulbs. This is a particular nuisance as a level having three sight level cavities necessitates an inventory of at least two light bulbs. Nevertheless, it is seldom that all the light bulbs in the level will burn out at one time. Accordingly, the aggravation of replacing burned out light bulbs is further compounded, in that replacement of burned out light bulbs will be necessitated at various times.